Near-Earth Asteroids

Asteroids which come within 1.3 AU of the Sun are considered near-Earth asteroids. It is assumed that these asteroids have been knocked free from the main belt due to asteroid collisions or the gravitational influence of the planet Jupiter, or are the remnants of short-period comets. The largest known near-Earth asteroid is Ganymed,
with an approximate diameter of 25.5 miles (41 kilometers).

There are three main characterizations of near-Earth Asteroids, named for famous examples of each:

Interesting Stuff

Several asteroids are confirmed to have moons orbiting them, including Ida (which the spacecraft Galileo took photographs of in a 1993 fly-by -- the moon was named Dactyl), and Eugenia (which was confirmed by the Canada-France-HawaiiTelescope on Mauna Kea in 1999). This discovery allows observers to make more concise estimates of mass because of the gravitational relationship between the primary asteroid and its moon. These new observations have shown that many asteroids are far less dense than previously thought.